Field of the Invention
Embodiments of the present invention generally relate to a method and an apparatus for controlling fluctuations in power and amount of power used at an electric load location and/or on an electrical grid.
Description of the Related Art
Energy demand at a commercial site, such as a business, or at home will vary over the time of day. In a typical home or hotel setting, there is a peak in the morning when the occupants get up and when the occupants return home at the end of the day. This typically creates two demand peaks during a normal day. Commercial buildings tend to follow different patterns depending on the nature of the business. For example, usage is typically low when a commercial building is closed, and may be relatively constant or fluctuate between moderate to high levels depending on the type of business when the building is open. For example, a car wash may have more fluctuations in its energy use than an office building in a moderate climate.
The cost to a utility for generating or purchasing electrical energy increases dramatically during periods of peak use versus periods of off-peak usage. In order to compensate for the higher peak-hours costs, utility companies often employ time of day-based rate schedules, charging a significantly higher rate for electrical energy (e.g., cost per kilowatt-hour (kW-hr)) consumed during peak usage hours as compared to energy consumed during off-peak hours. For example, homes and businesses may pay for electricity on a per-kilowatt hour basis with one rate applying during off-peak hours, and another, higher, rate applying during peak hours. The higher rates charged during peak usage periods can lead to significantly higher energy costs for the user, especially when the user's period(s) of high demand coincides with or falls within the interval set by the utility as peak hours.
Devices have been developed that help users reduce the cost of electricity purchases from the power grid by storing electricity in energy storage mediums, such as batteries, that can be “drawn down” during peak hours to reduce demand from the grid. The batteries can be charged during non-peak hours, thus reducing the total cost of electricity, and, during favorable conditions, electricity can even be sold back to the grid. This process is often referred to as “energy arbitrage,” which is generally the storing of energy at one time of day and then the discharging of energy at another time, effectively shifting energy consumption from one time period to another.
Energy storage mediums, especially battery energy storage, are expensive and, while various techniques are known by which an energy storage system can be used to optimize energy use at a business or home, such techniques are generally inefficient in applying stored energy to effectively control the energy use at an electric load location. Consequently, an impractical quantity of energy storage mediums are required at an electric load location to realize useful energy arbitrage. Generally, such energy storage systems use simple methods for controlling the charging and discharging of power provided to offset peak demands. For example, two approaches commonly used in energy storage systems include: Using a simple timer to control charge times of the energy storage system (typically during off-peak hours) and discharge times (typically during peak demand hours); and using a single demand set-point that the storage system reacts to while monitoring and controlling the energy use of the business or home location. A single demand set-point generally is a single level set-point to which the controlling element in an energy storage system will control during operation. Each of these approaches generally requires an uneconomical amount of energy storage capacity in order to offset demand peaks at the electric load location. Furthermore, use of a single demand set-point typically results in an energy storage system running out of energy storage availability due to over-reaction of the controlling components to the demand set point set by the controlling system. Thus, a need exists for power charge and discharge systems and methods that more effectively utilize the consumable energy storage medium components in an energy storage system.
At larger and/or more power usage intensive electric load locations it is often desirable to use more than one energy storage system to control the demand and/or reduce power fluctuations at the electric load location. Current solutions for these types of electric load locations entail multiple discrete energy storage systems, where if any piece of an energy storage system is damaged, the ability to control the power demand at the entire electric load location is at risk of becoming inoperable due to the system's inability to compensate to the change in power control.
Today's electric grid is typically undersupplied and over demanded at critical points during the day and at other times it is oversupplied and under demanded. With an increase in unstable renewable generation (e.g., wind and solar) and a decrease in the number of traditional generators, it is becoming more and more difficult for utilities and grid operators to reliably manage their transmission and distribution grids. One new phenomenon that is exacerbating these problems is the new energy demand of electric vehicle charging. Grid managers are not able to control when or where electric vehicles are charged, and the charging load can range from several kilowatts to around 100 kW, depending on the type of charging station and the number of users at the charging station. A single charging electric vehicle can add the load equivalent to multiple homes, or an office building, at an unknown time and in an unknown place along the electric grid. Charging electric vehicles can overload transformers and other distribution equipment, causing early failure and higher distribution costs, and add significant unpredictable load to the electric grid. Therefore, there is a need for power charge and discharge systems and methods that can account for the varying loads and unpredictable nature of charging electric vehicles, or other similar devices, and minimize their affect on the electric grid and power fluctuation seen at a local electric load location.